U.S. Pat. No. 5,886,822 discloses making an ophthalmic lens that presents a projection insert. Such a projection insert is constituted by an optical imager for shaping the light beams coming from an electronic and optical system for generating light beams based on an electronic signal, the system being of the miniature screen, laser diode, or light-emitting diode (LED) type. The optical imager directs the light beams towards the wearer's eye to enable the information content to be viewed.
That prior art optical imager includes a propagation prism, a counter-prism, a quarterwave plate, and a spherical Mangin mirror. The spherical Mangin mirror is a plano-spherical lens on which the spherical face has been made reflective by means of treatment with aluminum or the equivalent.
The imager also includes polarization separation treatment that can be implemented by depositing thin layers, either on the propagation prism, or on the counter-prism, or by means of a film bonded between those two elements.
The imager may be embedded in a lens by molding as described in patent document FR 2 828 743.
By causing optical beams to propagate parallel to the plane of the lens accompanied by reflection at 45°, such a projection insert presents thickness that is relatively large, assuming it is desired for the apparent size of the projected image to be sufficiently large and acceptable. This goes against obtaining a lens fitted in this way that also serves to correct vision. Given the curved correcting surfaces at the front and the rear of an ophthalmic lens and given the curvatures that depend on the vision correction to be provided, the overall thickness of the lens becomes unacceptable.
U.S. Pat. No. 6,384,982 proposes a display in which the light beams emitted by an optical element of a light beam generation system are introduced via an entry surface and directed towards the eye of the wearer so as to enable information content to be viewed, the light beams being reflected a plurality of times between two “reflection” faces between their entry into and their exit from the lens, said two reflection faces being faces of a transparent optical insert constituted by a light guide.
U.S. Pat. No. 6,474,809 also discloses making an ophthalmic display in which a reflective holographic element is provided in the lens or between two half-lenses. Both faces of the lens are then reflective and the light beams reflect thereon a plurality of times before reaching the holographic elements where they are directed towards the eye of the user.
Although those types of display enable a lens to be obtained of smaller thickness, they raise a problem of achieving a compromise between the display function and the vision correction function. The faces of the lens are involved in both functions, so for example it is impossible to change the radius of curvature of one face for vision-correction reasons without disturbing the display function. If they are also required to correct the user's vision, such ophthalmic displays can therefore be made in bespoke manner only. In practice, such displays thus cannot be reasonably adapted to a vision-correcting lens.